1. Field of the Invention
The present invention generally relates to electronic systems, and more specifically to systems using electromagnetic transponders, that is, transceivers capable of being interrogated in a contactless and wireless manner by a read and/or write terminal.
2. Discussion of the Related Art
Many communication systems are based on a modulation of an electromagnetic field generated by a terminal. They range from the simplest electronic tag used as a theft-prevention device to more complex systems where a transponder intended to communicate with the terminal when it is in its field, is equipped with calculation functions (electronic purse, for example) or data processing functions.
Electromagnetic transponder systems are based on the use of oscillating circuits comprising a winding forming an antenna, on the transponder side and on the terminal side. Such circuits are intended to be coupled by a near magnetic field when the transponder enters the field of the terminal. The oscillating circuits of the terminal and of the transponder are generally tuned to the same frequency corresponding to the excitation frequency of the oscillating circuit of the terminal.
In most cases, transponders have no autonomous power supply and extract the power supply necessary to their circuits from the high-frequency field radiated by the antenna of the terminal.
When a transponder needs to communicate with a terminal, the transponder may have to authenticate the terminal before accepting a data exchange. For example, in applications where the transponder is used as a payment means (be it in money or units of account), it may reserve payments to certain terminals. According to another example, a transponder of chip card type, associated with electronic equipment (for example, a personal digital assistant or a cell phone) identifies or authenticates a user in a communication with other electronic equipment (for example, a laptop or desktop computer).
Currently, authentication processes use cryptography algorithms and a data exchange between the terminal and the transponder. Such processes require significant power- and time-intensive calculations. Further, any cryptographic process is more or less sensitive to attacks aiming at discovering the secret of the authentication to hack the system.